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Query: UMLS:C0011849 (diabetes)
 277,896 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The juvenile form of diabetes, type-I diabetes mellitus, is, to our knowledge of today, an autoimmune disease with the hallmark of selective destruction of the insulin-producing beta cells in the endocrine pancreas. The slow, progressive process is in strong contrast with the sudden onset of clinical disease. The identification of target antigens has implications for both, better diagnostic at an earlier time as well as for new forms of therapy such as induction of tolerance or T-cell vaccination. Next to the direct products of the beta cell, insulin and proinsulin, two antigens of 38 resp. 64 kD molecular weight, have been identified. Other possible antigens include carboxypeptidase H and a heat-shock protein of 65 kD. The identity of the antigen recognized by islet-cell antibodies, the most frequently used marker for type-I diabetes mellitus, remains a subject of discussion.
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PMID:[Autoantigens in type-I diabetes]. 180 31

Using serum from a prediabetic patient as a probe, we screened 0.5 x 10(6) recombinants from a rat islet lambda gt11 expression library. One plaque-producing antigen reactive with this prediabetic serum was identified, subcloned, and sequenced. Analysis of the sequence reveals that the clone encodes a 136-amino acid fragment of carboxypeptidase-H (enkephalin convertase). Carboxypeptidase-H is a molecule expressed within islet secretory granules and neurendocrine cells. The patient whose antibodies recognize this recombinant molecule (termed DG-1) was negative for anti-DG-1 antibodies in 1984, developed the antibodies by 1986, and remained positive until the development of diabetes in 1988. To date, serum from 5 of 20 cytoplasmic islet cell antibody-positive relatives reacted with the expressed protein, while none of 14 control sera reacted. On Western blotting, the initial patient's serum used for the screening reacts with a 52-kDa antigen corresponding to the mol wt of the membrane form of carboxypeptidase-N. The current study has identified carboxypeptidase-H as an autoantigen recognized by serum of pretype I diabetes, and the methodology used should aid in identification of additional autoantigens associated with type I diabetes.
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PMID:Identification and cloning of a granule autoantigen (carboxypeptidase-H) associated with type I diabetes. 195 1

Mice homozygous for the fat mutation develop obesity and hyperglycaemia that can be suppressed by treatment with exogenous insulin. The fat mutation maps to mouse chromosome 8, very close to the gene for carboxypeptidase E (Cpe), which encodes an enzyme (CPE) that processes prohormone intermediates such as proinsulin. We now demonstrate a defect in proinsulin processing associated with the virtual absence of CPE activity in extracts of fat/fat pancreatic islets and pituitaries. A single Ser202Pro mutation distinguishes the mutant Cpe allele, and abolishes enzymatic activity in vitro. Thus, the fat mutation represents the first demonstration of an obesity-diabetes syndrome elicited by a genetic defect in a prohormone processing pathway.
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PMID:Hyperproinsulinaemia in obese fat/fat mice associated with a carboxypeptidase E mutation which reduces enzyme activity. 766 8

Type 1 diabetes is the result of an ongoing autoimmune response to specific proteins expressed by the insulin producing beta cells. Recently, a number of beta cell autoantigens have been identified. However, their role in mediating the diabetogenic response is not known. Here we assess the relative importance of a panel of beta cell autoantigens in the disease process. The approach was to inhibit T cell proliferation to a given autoantigen by either i.t. or i.v. injections, and then determine the effect this had on the diabetogenic response. We show that administering murine glutamic acid decarboxylase (GAD) to 3-week-old NOD females can reduce the frequency of insulitis and prevent the onset of diabetes. In contrast, carboxypeptidase H or peripherin do not induce a similar protective effect, suggesting that GAD has a critical role in the diabetogenic response. These results also suggest that GAD may provide a useful target for antigen-specific immunotherapy.
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PMID:Administering glutamic acid decarboxylase to NOD mice prevents diabetes. 788 40

Type 1 (insulin-dependent) diabetes mellitus is a T-cell mediated autoimmune disease with a number of different proteins being implicated as target autoantigens. A 38 kDa protein residing in the insulin secretory granule of insulinoma tissue is recognized by T-cell clones from a newly-diagnosed Type 1 diabetic patient. We have investigated the capacity of normal rat pancreatic beta-cell extracts and various subcellular fractions of transplantable RIN tissue to induce proliferation of T cells from non-obese diabetic (NOD) mice and H-2 identical NON.NOD-H-2g7 control mice. Normal rat islet beta-cell protein fractions induced intense, dose-dependent proliferation of NOD splenic T cells, but only marginal proliferative responses of NON.NOD-H-2g7 splenic T cells. To further localize the target antigens, four different subcellular fractions from RIN tissue were used as a source of antigen; here in particular the cytosolic proteins showed dose-dependent activation capacity with splenic T cells in NOD animals. These activities were absent in control mice. There was no proliferation after incubation with microsome preparations from other rat endocrine tissues. Purified carboxypeptidase H did not have any stimulatory activity on NOD T cells. Fractionation of the RIN cytosolic proteins showed a large number of different fractions eliciting proliferative activity. These results demonstrate that NOD T cells respond to a large number of potential islet beta-cell target antigens and it will be necessary to utilize NOD T-cell clones to identify the number and nature of these antigens.
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PMID:A multiplicity of protein antigens in subcellular fractions of rat insulinoma tissue are able to stimulate T cells obtained from non-obese diabetic mice. 831 41

In the short term (< 2 h), proinsulin biosynthesis is predominately glucose regulated at the translational level; however, the details at the molecular level behind this mechanism are not well defined. One of the major hindrances for gaining a better understanding of the proinsulin biosynthetic mechanism has been a lack of an abundant source of beta-cells that express a phenotype of regulated proinsulin biosynthesis in the appropriate 2.8-16.7 mmol/l glucose range as defined in normal pancreatic islets. In this study, we demonstrate that in the MIN6 cell line, specific glucose-regulated translational control of proinsulin biosynthesis is present in the appropriate glucose concentration range. In addition to that of proinsulin, the biosynthesis of the two proinsulin conversion endopeptidases, PC2 and PC3, was coordinately glucose regulated in MIN6 cells, whereas that of the exopeptidase, carboxypeptidase H, was unaffected by glucose. Proinsulin, PC2 and PC3 biosynthesis was specifically stimulated over that of total MIN6 cell protein synthesis above a threshold of 4 mmol/l glucose that reached a maximum rate between 8 and 10 mmol/l glucose. Glucose-induced proinsulin, PC2, and PC3 biosynthesis was rapid (occurring after a 20-min lag period but reaching a maximum by 60 min), unaffected by the presence of actinomycin D; and in parallel experiments, stimulatory glucose concentrations did not alter MIN6 cell total preproinsulin, PC2, or PC3 mRNA levels. Thus, short-term (< 2 h) glucose stimulation of proinsulin, PC2 and PC3 biosynthesis in MIN6 cells, like that in isolated islets, was mediated at the translational level. Intracellular signals for mediating glucose-stimulated proinsulin PC2 and PC3 biosynthesis translation in MIN6 cells also appeared to be similar to those in pancreatic islets, requiring glucose metabolism and a supporting role for protein kinase A. However, protein kinase C or a Ca(2+)-dependent protein kinase did not appear to be required for glucose-regulated proinsulin biosynthesis in MIN6 cells, as in islets. MIN6 cells are the first beta-cell line that indicate glucose-regulated proinsulin biosynthesis translation essentially identical to that in differentiated islet beta-cells and will be an important experimental model to better define the mechanism of proinsulin biosynthesis in detail.
Diabetes 1996 Jan
PMID:Glucose-regulated translational control of proinsulin biosynthesis with that of the proinsulin endopeptidases PC2 and PC3 in the insulin-producing MIN6 cell line. 852 57

Autoantibodies against several cytoplasmic autoantigens such as glutamic acid decarboxylase, heat shock protein 65, insulin, and carboxypeptidase H have been identified in the sera of patients with IDDM. To investigate whether type II DNA topoisomerase (TopII) is an autoantigen in IDDM patients, we have constructed a series of overlapping DNA TopII fragments that covered the entire length of this enzyme. These fragments were used as antigens to screen sera of IDDM patients. We have examined 195 Chinese IDDM patients (mean age 14.2 +/- 7.5 years, age at onset 9.2 +/- 6.4 years, duration of diabetes 4.6 +/- 3.4 years) and 51 nondiabetic individuals. The results showed that DNA TopII autoantibodies were detected in 49.2 and 47.2% of IDDM patients using purified TopII fragments and full-length TopII as antigens, respectively. The frequency of anti-TopII positivity was relatively stable irrespective of sex and disease duration. The patients were slightly older at onset and the prevalence of anti-thyroglobulin/anti-microsomal autoantibodies was twice that in the IDDM subgroup positive for anti-TopII than in IDDM patients who were negative for anti-TopII. We also characterized the epitopes of DNA TopII that were recognized by IDDM sera. Those epitopes resided mostly in three distinct domains. One resided in amino acid residues 1-147, another in amino acid residues 286-472, and the third in the COOH-terminal one-third of DNA TopII. Intriguingly, we found that these epitopes shared similarity (up to 36% identity and 63.6% homology) to previously identified epitopes of IDDM autoantigens.
Diabetes 1996 Apr
PMID:Characterization of human DNA topoisomerase II as an autoantigen recognized by patients with IDDM. 860 60

The hormone insulin remains the cornerstone of diabetic therapy since it is required for almost all cases of Type 1 and many cases of Type 2 diabetes. Since the discovery of insulin in 1921, much has been learned about its chemistry, structure and action as well as its production in the beta cell. Insulin is formed through a series of precursors, beginning with preproinsulin, the protein encoded in the insulin gene. These precursors direct the prohormone into the secretory pathway and ultimately into the secretory granules where it is converted into insulin and C-peptide. These products are stored and secreted together in a highly regulated manner in response to glucose and other stimuli. This review focuses on the recently discovered prohormone convertases, PC2 and PC3 (PC1), the enzymes responsible for the endoproteolytic processing of proinsulin to insulin and C-peptide in the beta cell as well as for the selective processing of proglucagon to glucagon in the alpha cell or GLP1 in intestinal L-cells. PC2 and PC3 are calcium-dependent serine proteases related to the bacterial enzyme subtilisin. They cleave selectively at Lys-Arg or Arg-Arg sites in precursors, generating products with C-terminal basic residues that are then removed by carboxypeptidase E, an exopeptidase. All 3 enzymes are expressed mainly in secretory granules of neuroendocrine cells throughout the body and in the brain. Inherited defects affecting the prohormone-processing enzymes have recently been found in association with unusual syndromes of obesity and other metabolic disorders.
Diabetes Metab 1996 Apr
PMID:The role of prohormone convertases in insulin biosynthesis: evidence for inherited defects in their action in man and experimental animals. 879 89

Physiological investigation has demonstrated that the central nervous system monitors body composition and adjusts energy intake and expenditure to stabilize total adipose tissue mass. Genetic variations in the signalling molecules involved in this regulatory system account for the heritable component of body fat content. The application of molecular techniques to rodent models of Mendelian obesity has resulted in the characterization of five loci at which mutations produce an abnormal accumulation of body fat. The genes at these loci include agouti, which encodes a molecule that antagonizes the binding of alpha melanocyte-stimulating hormone to its receptor; fat, which encodes carboxypeptidase E; tubby, which encodes a putative phosphodiesterase; obese, which encodes a circulating satiety protein; and diabetes, which encodes the receptor for the obese gene product. A more detailed understanding of the functional interrelationships of these genes should lead to important new insights into the causes and potential therapies for human obesity.
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PMID:Obesity genes and the regulation of body fat content. 893 64

Cpefat mice carry a mutation in the carboxypeptidase E/H gene which encodes an exopeptidase that removes C-terminal basic residues from endoproteolytically cleaved hormone intermediates. These mice have endocrine disorders including obesity, infertility, and hyperproinsulinemia-diabetes syndrome, but the etiology remains an enigma. Because studies have identified membrane carboxypeptidase E as a sorting receptor for targeting prohormones to the regulated secretory pathway for processing and secretion, the intracellular routing and secretion of pro-opiomelanocortin/adrenocorticotropin and growth hormone from anterior pituitary cells were investigated in Cpefat mice. In Cpefat mice, pro-opiomelanocortin was accumulated 24-fold above normal animals in the pituitary and it was poorly processed to adrenocorticotropin. Furthermore, pro-opiomelanocortin was secreted constitutively at high levels, showing no response to stimulation by corticotropin-releasing hormone. Similarly, growth hormone release was constitutive and did not respond to high K+ stimulation. Both pro-opiomelanocortin and growth hormone levels were elevated in the circulation of Cpefat mice versus normal mice. These data provide evidence that the lack of carboxypeptidase E, the sorting receptor, results in the intracellular misrouting and secretion of pro-opiomelanocortin and growth hormone via the constitutive pathway in the pituitary of Cpefat mice.
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PMID:Intracellular misrouting and abnormal secretion of adrenocorticotropin and growth hormone in cpefat mice associated with a carboxypeptidase E mutation. 914 34


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